Repeating elements and loops

Lines, distributions and anything that repeats — and the mapping that produced ONE line when the source had forty. The for-each construct maps a repeating source structure onto a repeating target structure, and the whole difficulty is that it must be applied at the RIGHT LEVEL. Set the loop on the wrong element and the mapping is still valid: it just emits one target element instead of forty, or forty identical ones, and the run succeeds. THE ONE-LINE FAILURE IS THE CLASSIC. An invoice arrives with forty lines and one is created. Nothing errors; the invoice exists, it is short, and the totals are wrong by an amount nobody notices until a reconciliation. The cause is almost always that the target element was mapped as a single occurrence rather than inside the loop, so the mapper filled it once from the first source row. The mirror failure is FORTY IDENTICAL…

In this module: Module 5 · Mappings and transformations

1. 1What a mapping really isFree preview
2. 2The mapper, practically
3. 3Required, optional and the empty element
4. 4Repeating elements and loops
5. 5Conditional mapping
6. 6Functions: strings, numbers and dates
7. 7Dates and time zones, carefully
8. 8Numbers, precision and currency
9. 9Lookups inside a mapping
10. 10Testing a mapping with real data
11. 11Namespaces, and the errors they cause
12. 12Keeping a mapping maintainable
13. 13What breaks: five mapping failures
14. 14Lab briefing · Map two schemas that disagree